In in vitro and animal models, it appears to have cytoprotective effects.[3][4][5][6]
Gene
Humanin is encoded in the mitochondrial genome by the
16S ribosomal RNA gene,
MT-RNR2.[7] Multiple paralogs are found in the nuclear genome (due to
nuclear mitochondrial DNA segments) and are named MTRNR2L followed by a number. It is not entirely sure whether these paralogous isoforms are completely unexpressed.[8]
Protein
The expressed peptide[9] contains a three-turn
α-helix, and has no symmetry.[9]
The length of the peptide depends on where it is produced. If it is produced inside the mitochondria it will be 21 amino acids long.[10] If it is produced outside the mitochondria, in the cytosol, it will be 24 amino acids long.[10] Both peptides have been shown to have biological activity.[10][11]
Other species
Humanin is the most well-
conserved of the mitochondria-derived peptides, found in such diverse species as humans,
naked mole rats, and
nematodes.[5] Overexpression of humanin in
Caenorhabditis elegans has been shown to extend the lifespan of that nematode by increasing
autophagy.[5]
The
rat,
Rattus norvegicus, has a gene, rattin (C0HLU6, "Humanin-like protein"), that encodes a 38 amino acid peptide homologous to humanin.[12] The two genes produce
cDNAs that show 88% sequence identity.[12] The peptides are 81% identical, with the carboxyl terminal sequence in rattin being 14 amino acids longer than in humanin.[12] Of the 24 amino acids in the rest of the rat sequence, 20 are identical to the amino acids in the human sequence.[12]
The mouse MT-RNR2 humanin ortholog is a
pseudogene, so no humanin is produced from the mtDNA. However, the nuclear genome harbors (like in humans) many copies of mitochondrial genomes, and one copy of the humanin homolog, Gm20594 (J3QJY3), is actively expressed.[13]
Function
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Extracellular interaction with a tripartite receptor composed of
gp130,
WSX1, and
CNTFR, as well as interaction with the
formyl peptide receptor 2 (formylpeptide-like-1 receptor) have been published.[15][16]
Intracellular interaction with BAX, tBID, IGFBP3, and
TRIM11 may also be required for the effects of humanin.[11][17][18][19]
Discovery
Humanin was the first mitochondria-derived peptide to be discovered.[5] Humanin was independently found by three different labs looking at different parameters. The first to publish, in 2001, was the Nishimoto lab, which found humanin while looking for possible proteins that could protect cells from
amyloid beta, a major component of
Alzheimer's disease.[7] The Reed lab found humanin when screening for proteins that could interact with
Bcl-2-associated X protein (Bax), a major protein involved in
apoptosis.[11] The
Pinchas Cohen lab independently discovered humanin when screening for proteins that interact with
IGFBP3.[17]
Research
Experiments using cultured cells have demonstrated that humanin has both neuroprotective as well as cytoprotective effects and experiments in rodents have found that it has protective effects in Alzheimer's disease models, Huntington's disease models and stroke models.[20]
Humanin is proposed to have myriad neuroprotective and cytoprotective effects. Both studies in cells and rodents have both found that administration of humanin or humanin derivatives increases survival and/or physiological parameters in
Alzheimer's disease models.[21][22] In addition to
Alzheimer's disease, humanin has other neuroprotective effects against models of
Huntington's disease,
prion disease, and
stroke.[23][24][25]
Beyond the possible neuroprotective effects, humanin protects against oxidative stress, atherosclerotic plaque formation, and heart attack.[26][27][28][29] Humanin activates
chaperone-mediated autophagy in a dose-dependent manner.[3] Humanin decreases production of inflammatory
cytokines, which is part of its anti-
apoptotic effect.[4] Metabolic effects have also been demonstrated and humanin helps improve survival of pancreatic beta-cells, which may help with
type 1 diabetes,[30] and increases insulin sensitivity, which may help with
type 2 diabetes.[31][6] In rats, the humanin analog appears to normalize glucose levels and reduce diabetes symptoms.[32]
Rattin shows the same ability as humanin to defend neurons from the toxicity of
beta-amyloid, the cause of degeneration in
Alzheimer's disease.[12]
Small humanin-like peptides are a group of peptides found in the mitochondrial 16S rRNA, and also possess retrograde signaling functions.
References
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Niikura T, Hashimoto Y, Tajima H, Ishizaka M, Yamagishi Y, Kawasumi M, Nawa M, Terashita K, Aiso S, Nishimoto I (March 2003). "A tripartite motif protein TRIM11 binds and destabilizes Humanin, a neuroprotective peptide against Alzheimer's disease-relevant insults". The European Journal of Neuroscience. 17 (6): 1150–8.
doi:
10.1046/j.1460-9568.2003.02553.x.
PMID12670303.
S2CID1345339.
^Tajima H, Kawasumi M, Chiba T, Yamada M, Yamashita K, Nawa M, Kita Y, Kouyama K, Aiso S, Matsuoka M, Niikura T, Nishimoto I (March 2005). "A humanin derivative, S14G-HN, prevents amyloid-beta-induced memory impairment in mice". Journal of Neuroscience Research. 79 (5): 714–23.
doi:
10.1002/jnr.20391.
PMID15678515.
S2CID25194143.
^Kariya S, Hirano M, Nagai Y, Furiya Y, Fujikake N, Toda T, Ueno S (2005). "Humanin attenuates apoptosis induced by DRPLA proteins with expanded polyglutamine stretches". Journal of Molecular Neuroscience. 25 (2): 165–9.
doi:
10.1385/JMN:25:2:165.
PMID15784964.
S2CID23766205.
^Sponne I, Fifre A, Koziel V, Kriem B, Oster T, Pillot T (January 2004). "Humanin rescues cortical neurons from prion-peptide-induced apoptosis". Molecular and Cellular Neurosciences. 25 (1): 95–102.
doi:
10.1016/j.mcn.2003.09.017.
PMID14962743.
S2CID20276062.